Low energy gamma rays from thermal neutron capture

The beam tubeP2 of the 4 MW FRM pool reactor was used as the neutron source for this nuclear spectroscopy study. An 8.5 and 13.5 cm lithium drifted germanium detector were used as gamma ray detector to measure the low energy prompt photon emissions from thermal neutron capture in 18 elements (12 rare earth elements) having aσ/A value greater than 0.1. The energy region was from 50–500 keV. Energy and intensity of the gamma ray lines are given.     

P-odd, P-even, and T-odd asymmetries in true quaternary fission of nuclei

The coefficients of P-odd, P-even, and T -odd asymmetries for a third and a fourth prescission particle emitted in the true quaternary fission of nuclei that was induced by polarized cold neutrons were studied on the basis of quantum-mechanical fission theory. By using non-evaporation (nonadiabatic) mechanisms of light-particle emission, these coefficients were compared with the analogous coefficients for prescission third particles emitted in the ternary fission of nuclei.     

Angular distribution of gamma rays from inelastic neutron scattering near threshold

The angular distributions of gamma rays following inelastic neutron scattering near threshold to the first excited states of the target nuclei were investigated experimentally and theoretically.Measurements used NaI(Tl) crystal detectors and natural targets of iron and cerium. Data were obtained for the angular distribution of gamma rays following inelastic neutron scattering by ⁵⁶Fe at the neutron center-of-mass energies E = 0.87, 0.90, 0.93, 0.95 and 0.99 MeV and by ¹⁴⁰Ce at E = 1.64, 1.67, 1.71, 1.75 and 1.87 MeV.The predictions for the gamma-ray angular distributions of the two following theories are determined: (i) the Satchler-Scheldon theory and (ii) the theory of Moldauer, specialized to the pure compound nucleus process and employing the “uncorrelated amplitude” assumption. Near threshold the predictions of the two theories are nearly the same.Theory and experiment are in good agreement for cerium at all energies at which angular distributions were obtained and for iron at E = 0.99 MeV but not at lower energies.Two general conclusions are drawn about measurements of the angular distribution of gamma rays following inelastic neutron scattering in medium and heavy nuclei at energies near threshold; (i) such measurements are not useful in deciding between the theories of Satchler-Sheldon and Moldauer, but (ii) they provide data for a sensitive test of the Hauser-Feshbach statistical assumptions.     

Resonance neutron capture gamma rays in 177Hf

Primary capture γ-rays have been studied for 38 ¹⁷⁷Hf neutron resonances with energies in the range 1–165 eV. Intensities were measured for 29 transitions ending at states with an excitation energy in ¹⁷⁸Hf up to 2050 keV. The analysis was facilitated by the previous knowledge of the spin and parity of all neutron resonances and of most low-lying states. For nine final levels, which had not previously been seen, information on J and π was deduced from the corresponding average intensities. The distribution of partial widths was fitted with a χ² function with ν = 1.38_?0.13^+0.18 degrees of freedom for E1 radiation and ν = 1.5_?0.40^+0.60 for M1 radiation. The average El reduced photon strength was found to be $\text{S}{}_{\mathrm{<mtext>El</mtext>}}\text{= 〈Γ}{}_{\mathrm{\gamma itij}}\text{/DE}{}_{\mathrm{\gamma }}{}^5\text{〉A}{}^{\mathrm{<mtext>?8</mtext><mtext>3</mtext>}}\text{= (4.8 ± 1.0) × 10}{}^{\mathrm{?15}}\text{MeV}{}^{\mathrm{?5}}$ and the ratio between El and Ml intensities equal to 5.5 ± 1.4. A comparison of this value for the El strength with those reported for other nuclei with A$\text{\$}\text{?}$= 100 showed that the intensities follow the A-dependence predicted by the Brink-Axel model. A non-statistical effect was observed, consisting of an enhancement of El transition probalilities to K = 2, 3 final states as compared to K = 0, 4 states.     

Parity violation at neutron p-wave resonances of238U and232Th and related questions

Parity violation effects have been studied at 40 neutron p-wave resonances of the even-even nuclei²³⁸U and²³²Th. Of these 11 show parity violation effects larger than 2 standard deviations, making parity violation a rather common phenomenon. Parity mixing up to 10% has been found. The root-mean squared matrix elements for parity violation derived from these resonances are M=0.58 (+0.50/-0.25) meV for²³⁸U, respectively 1.39 (+0.35/-0.38) meV for²³²Th.     

Ultra-high energy cosmic rays and prompt TeV gamma rays from gamma ray bursts

Gamma ray bursts (GRBs) have been proposed as one possible class of sources of the ultrahigh energy cosmic ray (UHECR) events observed up to energies ≳ 10²⁰ eV. The synchrotron radiation of the highest energy protons accelerated within the GRB source should produce gamma rays up to TeV energies. Here we briefly discuss the implications on the energetics of the GRB from the point of view of the detectability of the prompt TeV γ-rays of proton-synchrotron origin in GRBs in the up-coming ICECUBE muon detector in the south pole.     

Resonance conversion of gamma radiation in the radiative transitions between neutron resonances

The influence of the resonance conversion on the α-particle spectra in the reaction (n, α) in low-energy transitions between neutron resonances is discussed. Unusual α spectra from neutron resonances in the reaction ¹⁴⁷Sm(n, α)¹⁴⁴Nd are considered as an example of such influence. The calculation of resonance conversion coefficients was performed for the transitions from K shell in the free levels of P shell of Sm atom. The large effect of resonance in the radiative transitions for the nuclei and atomic electron shells is observed.     

用于n,γ混合场的新型脉冲中子探测器研究

新型脉冲中子探测器采用特殊工艺将两个PIN半导体组合而成.利用脉冲γ辐射研究了探测器对γ的响应；利用脉冲中子源研究了探测器对DT中了的响应，并与闪烁探测器进行了比较 .结果表明：脉冲中子探测器对脉冲γ辐射基本不灵敏，对脉冲中子辐射的灵敏程度依赖于中子辐射体，是一种用于n，γ混合脉冲辐射场中子测量的新型探测器. 关键词： 硅半导体 差分补偿 脉冲中子探测器 n γ混合场     

Averaged intensities of primary gamma rays after keV neutron capture in copper

The averaged intensities of high-energy gamma rays in copper have been measured with a Ge(Li) detector after the capture of 10–60 keV neutrons. The capture spectra represent the average strengths of transitions from a large number of resonances. They bear no relation to the thermal result, thus supporting the view that the latter proceeds through a non-compound nucleus mechanism. The ground state transition does not dominate the keV capture spectrum and the intensities indicate the presence of an E_γ³ energy dependence.     

Thermal-neutron capture gamma rays from natural calcium

Gamma rays from thermal-neutron capture in natural Ca and enriched ⁴⁰Ca were investigated with a 5 cm³ Ge(Li) detector. Many low-energy γ-lines have been found. More than 90% of the γ-rays result from capture in ⁴⁰Ca and about 5% from capture in ⁴⁴Ca. From the data a decay scheme of ⁴¹Ca and a partial decay scheme of ⁴⁵Ca were constructed. The Q-values for the reactions ⁴⁰Ca(n, γ)⁴¹Ca and ⁴⁴Ca(n, γ)⁴⁵Ca were determined as Q = 8363.4±1.0 and 7418.1±3.0 keV,respectively.In ⁴¹Ca, it is found that hole states preferentially decay to hole states, and single-particle states to single-particle states.     

Gamma rays from thermal neutron capture in gold

The thermal column of the 10 kW University of Maryland pool reactor was used as the neutron source for this nuclear spectroscopy study. A 40 cm³ lithium drifted germanium crystal was the gamma (γ) ray detector used to measure the high energy prompt photon emissions from thermal neutron capture. The energy region was from 2.6–7.0 MeV. New capture gamma ray lines were observed.     

Proper motion of gamma rays from microhalo sources

I discuss the prospects of detecting the smallest dark matter bound structures present in the Milky Way by searching for the proper motion of gamma-ray sources in the upcoming Gamma Ray Large Area Space Telescope all sky map. I show that for dark matter particle candidates that couple to photons the detection of at least one gamma-ray microhalo source with proper motion places a constraint on the couplings and mass of the dark matter particle.     

Detection of high-energy gamma rays from winter thunderclouds

A report is made on a comprehensive observation of a burstlike gamma-ray emission from thunderclouds on the Sea of Japan, during strong thunderstorms on 6 January 2007. The detected emission, lasting for approximately 40 sec, preceded cloud-to-ground lightning discharges. The burst spectrum, extending to 10 MeV, can be interpreted as consisting of bremsstrahlung photons originating from relativistic electrons. This ground-based observation provides the first clear evidence that strong electric fields in thunderclouds can continuously accelerate electrons beyond 10 MeV prior to lightning discharges.     

Overall picture of the cascade gamma decay of neutron resonances within a modified practical model

The intensities of two-step cascades in 43 nuclei of mass number in the range of 28 ≤ A ≤ 200 were approximated to a high degree of precision within a modified version of the practical cascade-gammadecay model introduced earlier. In this version, the rate of the decrease in the model-dependent density of vibrational levels has the same value for any Cooper pair undergoing breakdown. The most probable values of radiative strength functions both for E1 and for M1 transitions are determined by using one or two peaks against a smooth model dependence on the gamma-transition energy. The statement that the thresholds for the breaking of Cooper pairs are higher for spherical than for deformed nuclei is a basic result of the respective analysis. The parameters of the cascade-decay process are now determined to a precision that makes it possible to observe the systematic distinctions between them for nuclei characterized by different parities of neutrons and protons.     

Production spectrum of gamma rays in high energy interactions and high energy gamma ray intensity at 2900 m

An extended array of emulsion and lead plates has been exposed at Zugspitze for 6 months. The results of the measurements carried out on individual high energy cascades, and families of cascades allow the following conclusions to be drawn:

1. The vertical intensity of electrons andγ-quanta with energy > 1000 GeV on Zugspitze (2900 m) is 4.5/8.8 × 10^?10 cm^?2sec^?1ster^?1.
2. The energy spectrum of these particles has the shape of a power law with exponent — 1.85.
3. The production spectrum of secondary particles in individual interactions is derived, and it steepens with increasing primary energy. Using other evidence one may then conclude that this is due to an increase of multiplicity with primary energy.